Stripe subsciption

I have the stripe plugin built by bubble. I want to create a subscription per user where an administrator could subscribe several members at the same time. The problem is when I specify a quantity, it always charge the user for one item (I have tried with dynamic and static data).
The strangest thing is that when a user is subscribed and he clicks again on the same button (subscription button), the plan is updated with the good requested quantity.
Do you know why ?

I have added some screens (sorry for French langage in the stripe dashboard)!


Thank you very much